Is it possible to use Normal Maps with Tiled?
Not specifically, but Tiled doesn’t stop you from setting a normal map for the material you use in your game.
If you want it to be tile-specific you could use properties. This would only be visible within Tiled as a string though and would have to be handled on import.
is there a tutorial or documentation somewhere?
Or can I just use another Layer and later export 2 tilemaps (with normal maps on separate tilemap)?
I’m not sure how to use Properties for this.
The property would have the (relative) path to the normals texture as its value.
But you could also think about having seperate textures for each tile with a corresponding texture with the same name and then something appended (like _NORMALS) that would be linked to the correct material when importing the map into your game.